Electrical devices are often used at a wide range of operating environment temperatures. It is essential to the operation of an electrical device that it is used in such an operating environment where temperature is not above or below the rated operating environment temperatures given to the components of the device. If the operating environment temperature of the device is lower than stated in the operating instructions of a component, the component may become damaged. If the component remains undamaged despite of the low operating environment temperature, the operation of the device may, nevertheless, become disturbed. When the device is kept switched on long enough, the temperature around the device rises because of heat produced by components of good cold resistance. This makes poorly cold resistive components of the device operate in the desired manner. The temperature of the environment may refer to the air temperature inside the case in which the device is placed.
If a component of poor cold resistance is used in an environment possibly having a very low temperature, it is necessary to heat the device so as to make it function in the desired manner. U.S. Pat. No. 3,440,407, for example, discloses a multi-layer printed circuit board having in its inner layers a heating element which heats the circuit board and the components thereon. Since the heating element is placed in the inner layers, it is extremely difficult to direct the thermal power to an individual component. If the thermal power cannot be properly directed to the desired component, the operation of the components which are not wished to be heated becomes more difficult because of the excess heat. Since the heating of the printed circuit board requires wiring to be provided in the inner layers of the circuit board, the manufacturing costs of the board become relatively high. Furthermore, it is a disadvantage of the prior art temperature-controlled printed circuit board that for the heating element, the circuit board has to be provided with through holes. Furthermore, the prior art printed circuit board is prone to electromagnetic interference.